This application relates to electrical leads which are intended for implantation in the patient for numerous uses such as cardiac pacing or sensing, or any other desired use. Particularly, the lead of this invention is contemplated for use as part of a spinal lead system, in which, as is conventionally known, electrical current is applied to the spinal cord as a method of alleviating lower back pain. Such a lead is used to place an electrode in the epidural space of the spine. The lead may be adjusted in its position with current applied on an experimental basis until the patient reports the best paresthesia in a given position. At that point, or at a later time, the surgeon may implant, subcutaneously, a neurostimulator, and connect it to the positioned lead for transferring neurostimulating signals to the spinal cord.
In the prior art, a separate lead anchor is generally affixed in the area of the spinal lead's exit from the spinal column, and sutured to the patient. The purpose of this is, of course, to maintain the optimum position of the lead in the spinal column for maximum pain surpressing effect. The anchor may typically be sutured to the underlying muscle, with sutures also tied around the body of the anchor, while the lead itself is positioned within the anchor in telescoping relation thereto for retention.
Unfortunately, it has been found that, as the patient moves, it is possible for the lead to slide to a certain extent with respect to the lead anchor. This, in turn, results in a shifting of the position of the electrode in the epidural space, which may reduce the effectiveness of the pain-reducing electrical stimulation through the electrode. However, this problem has not been easily solved, because the precise positioning of the lead anchor on the lead cannot be exactly determined until actual implantation has taken place and after the electrode on the lead has been precisely positioned. Accordingly, the lead anchor cannot be preattached to the lead in a manner to effect permanent, non-sliding attachment, because of the unpredictability of the positioning of the lead tip and its electrode in the spine, coupled with the requirement for the lead anchor to be positioned at only about one possible position, at the spinal lead's exit from the patient.
For this reason, in the prior art, a lead anchor with a sliding connection with the lead that it retains has been mandatory.
In accordance with this invention, an improved electrical lead is provided, in which an attached lead anchor means may be adjustably positioned with respect to the lead. Nevertheless, the lead anchor cannot slide along the lead, so that an electrical lead may be provided for implantation with adjustable lead anchor positioning, but without the problem of the prior art of migration of the lead within the spine after the implantation procedure is complete. It can be understood that such migration is very unpleasant because it may require another operation to readjust the positioning of the lead, which of course is very traumatic to the patient and highly undesirable.